OK decision made: just bought my ticket, UA/A3 SFO-FRA-ATH-FRA-SFO, 3 hr connection time for both inbound and outbound, United operates w/ 777 those flights i was able to get the 17A both ways which according to seatguru should give me lots of legroom so i opted to buy cheapest non upgradeable and save miles for a business class award ticket SFO-NBO later in the year. Thank you all for the advice. It helped me make up my mind against LH Econ

Interestingly enough I am on a LH ticket for this itin even if non of the legs are operated by LH, one of the A3 flights is marketed as LH and the other is not, I am curious if I'll be getting any miles for those flights, although according to the mileage plus rules it might be unlikely....